Maintenance Tip of the Week: Vibration 11/16/2015

Maintenance Tip of the Week – Vibration 11/16/2015

Vibration is a leading indicator of engine, gearbox, shaft, and propeller problems. If, while underway, you feel an increase in vibration, or unusual vibration, the propulsion system must be inspected immediately as soon as it is safe to do so. Continued operation with damaged propellers or shafts will quickly ruin your gearbox and damage your engine (This type of repair is also usually very expensive).

ECA drive: A solution for low-draft situations


In last week’s articles, we detailed the various types of drives that are options with MarineDiesel’s engines as a complete package. There is, however, another type of drive that we will package, especially on vessels that will frequently be used near reefs, shallow rivers, or anywhere that has shallow draft: The ECA Articulated Shaft Drive.

The ECA drive is, on quick inspection, a conventional propeller, shaft, and rudder. Indeed, the drive can operate perfectly efficiently as such. On closer inspection, however, you will not a hydraulic lift and CV joint. These allow the shaft to trim up and down for use in shallow areas. Indeed, the drives were first developed for small fishermen who needed to navigate across or around shallow reefs. The drives allowed such navigation in areas that would damage other types of propulsion.

Manufactured in Spain by ECA, the drives are beginning to be noticed by naval architects. Indeed, we have recently shipped a number of engine / propulsion packages with the drives. Please see the video below for a better understanding of the ECA drives and how they work:

For more information on ECA drives, or for a custom quote for your project, contact your local MarineDiesel distributor or MarineDiesel direct.





Stern Drive Packages


The most common type of propulsion package that MarineDiesel sells is with stern drives as the propulsion type.


  1. Stern drives are highly versatile. They can be used in just about any mission or application.
  2. Stern drives are generally inexpensive.
  3. Stern drives can provide a very high top speed.
  4. Stern drives are generally easy to maintain or replace.
  5. Stern drives are manueverable at slower speeds.
  6. Gearboxes are usually integrated into the drive unit.

MarineDiesel packages two brands of stern drive with its’ engines, in different situations:

On recreational vessels, we can provide Mercury Bravo drives. Mercury Bravo drives give good performance while being inexpensive. However, they are typically not designed for commercial or heavy use. This is why we typically only recommend them on vessels that will operate under 200 hours per year. Bravo drives are limited to 400 hp applications (sometimes, depending on the vessel, 450 hp will work).

On commercial or military vessels, we provide Konrad stern drives. Konrad stern drives are engineered to take the punishment and abuse that commercial or military users require. With a MTBO of 2,500 hours, Konrad drives give top performance and reliability. Our entire engine range will work with Konrad drives.

When are other propulsion types more appropriate?

  1. On vessels requiring more than 500 hp.
  2. Low draft situations.
  3. Vessels over 14t displacement.

As with the other propulsion types, proper calculations are a must and require proper vessel information.

If you would like a complete stern drive propulsion package quoted with your engines, contact your local MarineDiesel distributor today for a custom quote, or contact us directly for assistance.





Surface Drive Propulsion Packages


Continuing from yesterday’s article about propulsion packages, there is one type of propulsion that will always provide the highest top speed on any vessel: Surface drives.

MarineDiesel has teamed up with France Helices to offer the France Helices SDS surface drives to our customers, as a package with our engines.

Of all of the propulsion types available in the market, surface drives will give the highest top speed and, in the case of articulated surface drives, the greatest level of control and maneuverability on high speed or high performance vessels. In layman’s terms, surface drives use the cavitation produced by the propellers as thrust, while minimizing drag, thus ensuring extremely high top speeds. They are designed to force a vessel to plane quickly, and efficiently. Of course, on high speed vessels, proper calculations are essential to achieving the required performance levels. France Helices specialize in designing propellers specifically intended to give required performance levels. In other words, the drives are customized to the vessel, and not the vessel customized to the propulsion.

When are surface drives appropriate?

  1. Any vessels required to achieve top speeds over 50 knots (In some cases, surface drives are the only way to achieve these speeds).
  2. Vessels that will operate in shallow draft areas.
  3. Vessels that will operate in dirty or polluted water.
  4. Vessels that require extremely high levels of maneuverability, crash stop, or acceleration.
  5. Vessels that will operate in rough seas.

When are surface drives not the best choice?

  1. On vessels that will operate at speeds below 30 knots a substantial amount of the time.
  2. On vessels used for boarding (like pilot boats).
  3. On vessels that will operate with people in the water nearby (rescue craft, dive boats).
  4. On vessels that are overweight by design (large displacement variations).
  5. On vessels that have displacement or semi-displacement hulls.

On surface drive equipped vessels, the calculations can be somewhat involved, requiring a substantial amount of information on the vessel. Visit the France Helices website for more information.

If you would like a quote on a performance package with MarineDiesel engines and surface drives, contact your local MarineDiesel distributor or dealer today, or MarineDiesel directly, for a customized quote.







Water Jet Propulsion Packages


MarineDiesel packages its’ engines with a wide variety of different propulsion options, whether conventional propeller, surface drives for extremely fast vessels, stern drives, or water jets. Our customers often like the “One Stop Shop” ability, and we have made arrangements to provide these packages at full warranty.

As with any propulsion method, proper calculations are essential to achieving required vessel performance. Ever drive and propulsion maker has their own calculation programs for their drive types, and it is important that required vessel information is correctly provided to ensure the proper matching of engine to drive.

Water jets have some distinct advantages over other types of propulsion systems:

  1. Safety is the most important advantage of water jets. Without propellers spinning in the water, vessels are, inherently, much safer. The propulsion arises from an impeller, located within the drive unit. This makes water jets ideal for ski boats, rescue craft, lifeboats, dive boats, or any other vessel that will be operating in close proximity to people.
  2. Very often, water jets can be operated without a gearbox (this is usually dependent on vessel displacement), thus saving money on installation.
  3. Most water jets are relatively easy to maintain, with the primary maintenance required being the clearing of the tunnel and intakes, along with the inspection of the impeller.
  4. Water jets have good maneuvering capability at slower speeds.
  5. Water jets can provide a high top speed, though, in most cases, lower than surface drives or stern drives. However, water jets do not face the same displacement limits as other propulsion types.

MarineDiesel primarily packages our engines with two brands of water jets (Though our engines will work with any brand of jet, as long as the size is correct):

Alamarin, made in Finland, on smaller vessels.

Doen, made in Australia, on larger vessels.

Both of these brands have proven to be reliable and easy to maintain over their respective life cycles. Additionally, we can sometimes offer Hamilton, Kamewa, or other brands of water jet through our distribution and dealer network (Most of our distributors represent multiple brands of marine equipment).

For your next project, contact your local MarineDiesel distributor or MarineDiesel directly for a customized quote on an engine and propulsion package.




Vessel Performance and Load



“Load” is one of those terms that gets thrown around in the marine industry, and the meaning is often blurred. What, exactly, is meant buy load, and how does it impact vessel performance.

Load can refer to either:

  • Engine load
  • Vessel load (tied to displacement)

These two things are also tied together.

Most high speed vessel are designed with a planning hull. In other words, the hull is designed to lift itself out of the water when power is introduced. It is a question of physics and opposing forces. In absolute simplest terms, the hull is experiencing:

A force downwards. This is displacement, or the weight of the boat. If more weight is added, the greater the force necessary to lift the boat.

A force backwards. This is resistance. As the propulsion system pushes forwards, the resistance increases. Additionally, anything sticking in the water, like the drive, rudder, propeller, or spray rails, produces drag, which increases resistance.

A force upwards. This is buoyancy.

A force forward. This is propulsion.

There are other forces and impacts on performance, such as trim of drives, wind, intakes, etc. The above are the most important.

So, as is evident, vessel performance is a question of balance. In order to make the boat move forward and up, enough power needs to be provided to overcome these forces. There is no magic or voodoo involved. It is simply a question of physics. Depending on the extent of the problem, a solution may or may not be able to be found.

So, on vessels with performance problems, the first diagnostic is usually weight. More weight means more displacement means the engine must work harder to make the boat plane. This is engine load. This is also why naval architects often pull their hair out at design changes. Any additional weight will impact performance. Put a marble floor in a recreational yacht? Performance will suffer. Extra guns and ammunition on a military boat? Performance will suffer. Add 10 additional passengers on a water taxi? Performance will suffer.

Load on the engine. Load on the hull. In both cases, speed, maneuverability, and overall performance take a hit.






MarineDiesel VGT + Konrad Performance Package



MarineDiesel has teamed up with Konrad to offer the most reliable engine and sterndrive high performance package in the marine market today.

Sterndrives have some distinct advantages as a propulsion system over other types of drive. They are capable of producing very high speeds and yet, can offer good maneuverability at slower speeds. Traditionally, the Achilles Heel of sterndrive systems has been their reliability and high cost of maintenance. They just could not stand up to the high torque produced by diesel engines and heavy, continuous use by commercial or government users.

Until Now…

Konrad is recognized as producing the only reliable sterndrive propulsion system that can withstand heavy commercial or military use.


The Konrad sterndrive can last over 2,500 hours between overhauls.

This makes the Konrad sterndrives the only real option available to commercial users. Drives produced for use with gasoline engines, or for intermittent recreational use generally require overhauls in as few as 400 hours. Though often inexpensive to purchase, they can quickly become extremely expensive to own over the long term. For commercial users, this adds up to many thousands of dollars of expenses over time.

The sheet below illustrates the cost advantages of Konrad over other brands of sterndrive.

When paired with MarineDiesel’s VGT Series of engines,

Please take a look and send us a note if you would like to have a custom quote on a package for your vessel.

Konrad / VGT Package 

Konrad / VGT Drawing







Celebrate Industrial Engine Week! Airboats



Today is the final day of our industrial engine week, and we focus on a niche market that has been up-and-coming for MDPT over the last couple of years: Airboats. Hmmm…


Correct. Airboats are a special case that is handled by MDPT rather than the larger MarineDiesel group because airboats are a hybrid of sorts. They are boats, but they use engines that are engineered for use on land. This makes them unique in the marine world.

Traditionally, airboats were simple vehicles: A shallow, flat bottomed boat with a (usually) used aircraft engine mounted astern that featured a direct coupling to an aircraft propeller straight off the flywheel. Ratios were inexact, with propeller pitch largely used to control performance levels.

Modern airboats bear little more than a casual resemblance to these old vessels. Modern airboats can now be equipped with climate controlled cabins, gun positions for military use, and are always equipped with modern, compact and high powered engines. Propellers are designed with lightweight composites, and there are complex gear or belt drive systems that can include variable gear ratios. Indeed, some airboats are now equipped with contra-rotating dual props that provide huge amounts of torque and extremely high speeds.

Airboats are often commonly seen in the Everglades, or on TV shows like “Swamp People”, and so on. They handle conditions in swamps quite well, being shallow draft and not having any propeller to run aground or get snagged. However, there are many other applications for airboats, and this niche market is booming: Military use for patrol, rescue, use on ice. All of these uses are now common.

For more information:

Leppek, Adam P., “Optimization of an Airboat Design” (2012). Honors Theses. Paper 2180. offers a good and interesting overview of modern airboat design and why airboats are well suited for their application.

MDPT is at the forefront of powering some of these cutting-edge designs. Our marine heritage serves us well in providing specialized engines for airboats. As we mentioned earlier, airboats are a hybrid of sorts. They use engines designed for use on land, but they are exposed to the harsh marine environment. We have the ability to combine these two fields of expertise into a single, customized and application-specific product, with appropriate injectors, connectors, and cooling systems. We also work very closely with the drive manufacturers, propeller manufacturers, and designers to offer complete airboat propulsion packages.

We have completed airboat projects in Russia, Finland, the USA, Australia, and Thailand, and this market segment is becoming a specialty of MDPT. Contact us today on your next project, but please see below for some previous MDPT installations.

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Drives: Which to choose?



Many of MarineDiesel’s engines are sold as vessel performance packages, as a complete unit: Engine, Gearbox, and Drive, ready to install. Of course, you can always purchase an engine from us and install your own equipment, but packaging allows the shipyard to combine installation, commissioning, and after sale service into a package easily service by our trained technicians, often at a far lower cost than buying each component separately (Since we buy far more gearboxes and drives per year than the average shipyard and most of our partners pass warranty expense to us, we can sometimes deliver components at a lower price.)

This brings up the question: What type of propulsion should I use on my vessel?

There is no single answer other than, “It depends on how the vessel will be used.”

Each propulsion method has strengths and weaknesses.

For instance, on single engine installation, surface drives are not a good option due to torsional pull. On these vessels, a stern drive or water jet should be considered.

MarineDiesel has put together packages with all of the major drive types. What should you choose? See below.

Sterndrive: good trim and reverse. Good box size for davit operation. Traditionally not strong but Konrad and MD is. More drag than surface drive. Good steering. Easy to install and small inside build dimension. Cheap propellers. Normally integrated transmission (not Konrad). Trolling function with MD, joystick control, crash stop. Low cost.
Waterjet: Safety aspects, no propeller. Will not work if there is too much debris. Bad efficiency in low and mid range. Crash stop. Very durable. No trim capability. Must in most cases use transmission. Expensive. Good maneuverability.
Surface drive: Highest speed and most durable in most cases. Expensive propellers. Poor slow speed performance. Difficult to handle torque response in single engine installation. Must use transmission. Can be expensive.
Pod system: Easy to install. No trim function. Falls off on impact, expensive to replace. Designed for pleasure use. Good steering and available with joystick. Very expensive.
Shaft setup: Durable. Needs transmission. Medium efficiency. Complex for boat builder to install. Good reverse and medium steering. No trim.